Aluminum alloy composition, article and method of use

ABSTRACT

An aluminum alloy composition consists essentially of controlled amounts of iron, silicon, copper, manganese, magnesium, titanium, zinc, zirconium, and free machining elements with the balance being aluminum and incidental impurities. The alloy provides improvements in combined strength, corrosion resistance, machinability, and brazeability. A component or article made from the aluminum alloy can be machined to the right configuration and can be brazed to another component to form a high quality brazed joint. In addition, the article can withstand corrosive environments and has the necessary mechanical properties to interface with other components. The alloy is adapted for particular use as a component in a heat exchanger assembly, such as a connector block having one or more machined surfaces or passageways.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 37 National Stage of PCT/US99/10447 filed May 19,1999, which is a continuation-in-part of application Ser. No. 09/081,452filed May 19, 1998 now U.S. Pat. No. 6,065,534.

FIELD OF THE INVENTION

The present invention is directed to an aluminum alloy composition, anarticle made from the composition and a method of use and, inparticular, to a composition which combines the properties ofmachinability, brazeability, corrosion resistance and strength.

BACKGROUND ART

In the prior art, the use of aluminum alloy compositions in heatexchanger applications is well known. Aluminum alloys are used for heatexchanger headers, tubing, fins and connector blocks. Typically, theconnector blocks are brazed to the header to facilitate the hookup offluid supply and takeaway lines of a system requiring fluid cooling,e.g., an air conditioning system.

When manufacturing the heat exchanger assemblies, the components areoften clamped together and furnace brazed using either clad materials,filler brazing materials or a combination of both.

One significant problem that occurs during the manufacturing of theassembly is the formation of an inferior brazing joint between theconnector block and the heat exchanger header. Prior to brazing, theconnector blocks are often machined and combined with fasteners tofacilitate connection to the fluid supply or takeaway lines. Because ofthe physical property requirements associated with the machining and thefastener use, prior art connector blocks are usually made from AA6000series aluminum alloys. These types of aluminum alloys exhibit poormachinability and are not easily brazed due to their high magnesiumcontent, especially in a controlled atmosphere brazing process.Consequently, it is often difficult to obtain a high quality brazedjoint between the connector block and another component of a heatexchanger assembly. Utilizing a more brazeable alloy such as a standardor commercial AA3000 series alloy does not present an acceptablealternative as a material for connector block use. The AA3000 seriesalloys, while being brazeable, are generally too soft to adequatelymachine or have the necessary mechanical properties to facilitatemechanically fastening the connector block to other components.

As such, a need has developed to provide an improved composition forheat exchanger application or other uses where machinability,brazeability, strength and corrosion resistance are required. Inresponse to this need, the present invention provides an improvedaluminum alloy composition and an article made therefrom which combinesmachinability, strength, corrosion resistance and brazeability. Theinventive aluminum alloy article has the required mechanical propertiesmaking it especially suitable for use as a heat exchanger component. Thealuminum alloy composition and article also facilitate brazing processeswhen assembling the inventive article with other components.

SUMMARY OF THE INVENTION

Accordingly, it is a first object of the present invention to provide analuminum alloy composition exhibiting machinability and brazeability.

Another object of the present invention is to provide an aluminum alloycomposition having good corrosion resistance and mechanical properties.

One other object of the present invention is to provide an aluminumalloy article made from the inventive composition.

A still further object of the present invention is to provide a methodof brazing the aluminum alloy article.

Other objects and advantages of the present invention will becomeapparent as a description thereof proceeds.

In satisfaction of the foregoing objects and advantages, the presentinvention provides an aluminum alloy composition consisting essentiallyof, in weight percent, up to about 0.6% silicon, up to about 1.2% iron,up to about 0.7% copper, between about 0.1 and 1.8% manganese, up toabout 1.5% magnesium, up to about 0.4% chromium, up to about 0.4% zinc,up to about 0.2% zirconium, between about 0.03 and 0.4% titanium, and atleast one free machining element selected from the group consisting ofbismuth, indium and tin or a compound thereof, wherein each of thebismuth and tin are up to about 1.5% and the indium ranges between about0.05 and 0.5%, with the balance being aluminum and incidentalimpurities.

The alloy composition has more preferred limits wherein the silicon isup to about 0.2%, the iron is up to about 0.7%, the copper is up toabout 0.5%, the manganese ranges between about 0.2 and 1.7%, themagnesium is up to about 0.8%, the chromium is up to about 0.2%, thezinc is up to about 0.25%, and the titanium ranges between about 0.03and 0.3%. The ranges of the at least one free machining element arefurther defined wherein tin and bismuth are each up to about 1.3% andthe indium ranges between about 0.05 and 0.3%.

In another embodiment, the silicon ranges between about 0.03 and 0.12%,the iron ranges between about 0.03 and 0.4%, the copper ranges betweenabout 0.01 and 0.5%, the manganese ranges between about 0.5 and 1.6%,the magnesium is up to about 0.7%, the chromium is up to about 0.1%, andthe titanium ranges between about 0.03 and 0.2%. The ranges of the atleast one free machining element are further defined wherein tin andbismuth are each up to about 1.0% and the indium ranges between about0.05 and 0.2%. Other embodiments are described below.

In yet another embodiment, the alloy composition has limits wherein thesilicon ranges between 0.01 and 0.15%, the iron ranges between 0.01 and0.5%, the copper, ranges between 0.01 and 0.4%, the manganese rangesbetween 0.2 and 1.7%, the magnesium is from zero up to 0.4%, an amountof chromium is up to 0.2%, an amount of zinc is up to 0.25%, an amountof zirconium is up to 0.3%, titanium ranges between 0.03 and 0.3%, andan amount of at least one of tin and bismuth is up to 1.3%.

The invention also includes an article made from the inventive alloycomposition. A preferred article is one that is machined and brazed. Anexample of such an article is a heat exchanger component which includesat least one machined portion such as a passageway, recess, seat,threaded portion or the like, e.g., a heat exchanger connector block.The component can include more than one passageway or machined portionand fasteners secured thereto to facilitate connecting the component toother components or structure.

The invention also comprises the article in combination with anothercomponent, for example, a connector block and a heat exchanger assemblywherein the assembly has cooling tubes, fins, headers and fluid supplyand takeaway lines.

A further aspect of the invention includes an improved brazing processwherein the inventive article is brazed using a flux. The articlepermits effective brazing with minimal amounts of flux.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the drawings of the invention wherein:

FIG. 1 is a partial schematic drawing showing a heat exchanger assemblywith an exemplary connector block made from the inventive composition;

FIG. 2 is an end view of the assembly of FIG. 1; and

FIG. 3 shows another embodiment of the inventive article.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention offers significant improvements in the field ofaluminum alloys compositions and articles made therefrom such as heatexchangers components, heat exchanger assemblies and brazing methods.The invention overcomes the dilemma facing engineers and designers whenseeking an aluminum alloy composition for a particular application thatrequires a combination of machinability, strength, corrosion resistanceand brazeability.

The aluminum alloy of the invention is ideally suited as an article foruse in an application requiring strength, brazeability, machinabilityand corrosion resistance. One particular application for the inventivealloy is a heat exchanger component that is machined, brazed, subjectedto corrosive environments and subjected to mechanical forces formechanical attachment to other heat exchanger components. One componentparticularly adapted as the inventive aluminum alloy article is aconnector block that links the inlet and outlet of a heat exchanger tocooling fluid supply and takeaway lines. These connector blocks areoften extruded shapes and require machining operations to form one ormore passageways therein as well as other recesses or configurations inthe connector block body like o-ring seals and seats with good surfacefinish to prevent leakage. Although the connector blocks can beextruded, they could also be forged or subjected to other forms of hotdeformation to form the desired shape.

Having the combined properties of machinability, brazeability, strengthand corrosion resistance in an aluminum alloy composition and an articlemade therefrom is unexpected when compared with known prior art alloysexhibiting only some of the desired properties. For example, machinablealloys such as AA6262 have poor brazeability. Brazeable alloys such asstandard or commercial AA3000 series alloys do not have the strength normachinability for use as an article that is machined, brazed andsubjected to mechanical forces such as torques.

The properties of machinability, brazeability, strength and corrosionresistance are related to the controlled compositional limits of theinventive aluminum alloy and its article form. In one aspect, the alloyhas controlled amounts of iron, silicon, copper, manganese, chromium,zinc and titanium. The term “amount” is intended to mean a finite amountof the named alloying element in a specified percentage which is deemedto be greater than percentages normally classified as incidentalimpurities in aluminum alloys. Another aspect of the alloy compositionincludes controlled levels of magnesium wherein the alloy may be eithermagnesium-free or may include a defined magnesium amount. In yet anotheraspect, at least one of bismuth, indium and tin are included in amountseffective to provide the enhanced machinability without the loss ofother properties, particularly mechanical properties. Zirconium is addedfor strength and corrosion resistance. Ranges of the various elementsare detailed below in terms of broad and more narrow limits.

In its broadest embodiment, the inventive aluminum alloy consistsessentially of, in weight percent, of the following composition: up toabout 0.6% silicon; up to about 1.2% iron; up to about 0.7% copper;between about 0.1 and 1.8% manganese; up to about 1.5% magnesium; up toabout 0.4% chromium; up to about 0.4% zinc; up to about 0.2% zirconium;between about 0.03 and 0.4% titanium; and one or more free machiningelements set forth in an amount effective to improve machinability ofthe alloy with the balance being aluminum and incidental impurities. Thefree machining elements can be selected from the group consisting oftin, indium and bismuth and compounds thereof. The tin and bismuth caneach range up to about 1.5% and the indium can range between about 0.05and 0.5%. Unless otherwise noted, all percentages listed below are inweight percent.

A preferred embodiment of the inventive alloy further defines certainelements wherein the silicon is up to about 0.2%, the iron is up toabout 0.7%, the copper is up to about 0.5%, the manganese ranges betweenabout 0.2 and 1.7%, the magnesium is up to about 0.8%, the chromium isup to about 0.2%, the zinc is up to about 0.25%, and the titanium rangesbetween about 0.03 and 0.3%. The at least one free machining elementranges are further defined as up to about 1.3% for the tin and bismuthand between about 0.05 and 0.3% for indium.

In a more preferred embodiment of the invention, the silicon rangesbetween about 0.03 and 0.12%, the iron ranges between about 0.03 and0.4%, the copper ranges between about 0.01 and 0.5%, the manganeseranges between about 0.5 and 1.6%, the magnesium is up to about 0.7%,the chromium is up to about 0.1%, and the titanium ranges between about0.03 and 0.2%. The at least one free machining element ranges arefurther defined as up to about 1.0% for the tin and bismuth and betweenabout 0.05 and 0.2% for indium.

An even more preferred embodiment defines the alloy wherein the siliconis between about 0.03 and 0.09%, the iron is up to about 0.15%, thecopper ranges between about 0.1 and 0.4%, the manganese is between about1.0 and 1.6%, the magnesium ranges from an essentially magnesium freecomposition, i.e., less than 0.01%, to up to about 0.3%, the titaniumranges between about 0.1 and 0.2%, and the tin is up to about 0.75%.

In another embodiment, the inventive aluminum alloy consists essentiallyof a finite amount of silicon up to about 0.2%, a finite amount of ironup to about 0.7%, and a finite amount of copper up to about 0.5%.

A further embodiment of the inventive alloy further defines certainelements of the composition wherein the silicon ranges between about0.01 and 0.15%, the iron ranges between about 0.01 and 0.5%, the copperranges between about 0.01 and 0.4%, and the magnesium is from zero to upto 0.4%.

In yet another embodiment of the invention, the copper ranges between0.03 and 0.4%, and the magnesium is from zero to up to 0.35%.

One other embodiment defines the alloy wherein the iron ranges between0.03 and 0.15%, and the copper ranges between 0.2 and 0.4. It should beunderstood that ranges or limits of one embodiment may be combined withor substituted for other embodiment amounts. More specific embodimentsare identified in Table I wherein the ALLOYS include the listed elementswith the balance being aluminum and incidental impurities.

TABLE I ALLOY Si Fe Cu Mn Mg Cr Ni Zn Ti Bi In Sn Zr A .16 .60 .09 1.07<.01 .27 <.01 .03 .04 <.01 <.01 <.01 .10 B .12 .14 .27 1.38 .17 .19 <.01.03 .04 <.01 <.01 <.01 .10 C .10 .10 .28 1.47 .22 .19 <.01 .03 .05 1.05<.01 <.01 .10 D .10 .10 .29 1.42 .17 .19 <.01 .03 .04 <.01 <.01 .74 .10E .10 .12 .29 1.38 .19 .19 <.01 .03 .04 <.01 .14 .13 .10 F .17 .59 .091.12 <.01 .27 <.01 .03 .04 <.01 .15 .13 .09 G .17 .63 .08 1.17 <.01 .27<.01 .03 .05 .79 <.01 <.01 .10 H .16 .61 .09 1.13 <.01 .27 <.01 .03 .04<.01 <.01 .74 .10 I .20 .69 .29 1.53 .08 .20 <.01 .02 .04 <.01 <.01 <.01<.01 J .19 .71 .29 1.31 .09 .21 <.01 .02 .04 <.01 .17 .16 <.01 K .19 .66.28 1.36 .08 .17 <.01 .03 .03 .80 <.01 <.01 <.01 L .20 .65 .29 1.41 .09.18 <.01 .03 .04 <.01 <.01 .79 <.01 M .20 .64 .29 1.40 .10 .17 <.01 .03.04 .69 <.01 .47 <.01 N .20 .66 .29 1.38 .08 .17 <.01 .03 .04 .38 <.01.34 <.01 O .06 <0.1 0.3 1.50 <0.01 <0.01 <.01 0.025 .15 0.8 <.01 <.01.10 P .06 <0.1 0.3 1.50 <0.01 <0.01 <.01 0.025 .15 0.47 <.01 0.36 .10 Q.06 <0.1 0.3 1.50 <0.01 <0.01 <.01 0.025 .15 <.01 <.01 0.8 .10

The inventive alloy is particularly useful as a connector block for usein a heat exchanger application, e.g., a condenser. The connector blockis made from the inventive alloy and has at least one machined portionand further having an inlet and an outlet for the passage of fluidthrough the connector block and to or from the heat exchanger. Theconnector block can have more than one inlet and outlet or passagewaydepending on the particular heat exchanger design and application. Forexample, the connector block could have a connector block body havingone inlet passageway interconnecting a source of inlet fluid and theheat exchanger, and a second outlet passageway directing fluid from anoutlet of the heat exchanger to outlet tubing downstream of theconnector block.

The connector block can also have threaded studs extending from theconnector block body, the studs interfacing with another body orconnector that is used to facilitate attachment of fluid supply andtakeaway lines to the connector block or provide structural support,e.g., attach the heat exchanger to an adjacent structure.

FIGS. 1 and 2 illustrate an exemplary connector block 10 in combinationwith a heat exchanger 20. The heat exchanger 20 is illustrated with oneheader 21 (the other header not shown), cooling tubing 25 and fins 27.Although not shown, the header 21 has internal baffles to direct thefluid passing through the tubing 25 on its journey through the entireheat exchanger for the proper cooling.

The connector block 10 has a connector block body 1 divided into aninlet portion 3 and an outlet portion 5. The inlet portion 3 has aninlet opening 7 and an outlet opening 9 defining a passageway 8, theopening 9 aligned with an opening 22 in the header 21 of the heatexchanger 20 via the tubing 12. Fluid enters inlet 7, passes through theinlet portion 3 and into the header 21 via the tubing 12 for cooling.

The outlet portion 5 has an inlet 11 and an outlet 13 defining apassageway 14, the inlet 11 in communication with an opening (not shown)in the header 21. Cooled fluid exits the header 21 and passes throughthe outlet portion 5 by entering the inlet 11 and exiting the outlet 13to begin another fluid cycle, e.g., a refrigeration cycle.

The connector block body 1 is shown with a pair of threaded studs 15,each stud threaded into a complementary threaded bore in the body 1. Thestuds are used to align and attach a mating connector (not shown) whichcan hook up fluid supply and takeaway lines to the connector block 10 orprovide structural support, e.g., attach a condenser to an automobilebody. It should be understood that other connector block configurationscan be utilized with the alloy of the invention. For example, a separateconnector block could be used for each inlet to the header and theheader outlet. The connector block could be designed without the needfor tubing 12 or could have different studs or other attachment devicesto facilitate connector block hookup to either of the inlet or outlettubing of a system requiring fluid cooling.

The connector block passageways 8 and 14 are formed by machining theconnector block body 1. The passageways can also include lips, steps,seats, threads or other machined configurations as deemed necessary tointerface with heat exchanger components or other fasteners, connectorsor the like.

FIG. 3 shows another connector block configuration designated by thereference numeral 30 and having a body 31 with a machined passageway 33therethrough. The passageway 33 has a first opening 35 and a secondopening 37, the opening 37 designed to align with an opening in aheader. Depending on the direction of flow of fluid through thepassageway 33, one of the openings, either 35 or 37, is an inlet and theother becomes an outlet. Although passageways are depicted in FIGS. 1-3,the inventive article could be formed with one or more passagewaystherein by an operation other than machining, e.g., extrusion or thelike. In this instance, the article may then be subjected to machining aportion thereof to meet final dimensional tolerances, finishes or thelike. Again, other configurations can be utilized providing that thearticle is need of some degree of machining.

With reference back to FIG. 1, the connector block is shown with brazedportions 17 wherein the connector block is secured to the header 21 fora fluid-tight fit. The connector block 10 can be brazed to the heatexchanger by any known techniques, but controlled atmosphere furnacebrazing is preferred. The appropriate cladding material or filler metal,e.g., an AA4000 series aluminum-silicon filler metal, can be used aspart of the brazing process. Using the inventive alloy for the connectorblock 10 permits a low level of flux to be used during the brazingcycle, thereby reducing flux consumption and cost. For example, whenbrazing a prior art AA6000 series connector block to a heat exchanger,the amount of flux required can be as high as 100 to 200 g/m² of flux,wherein m² represents the area to be brazed and g is the weight in gramsof flux. Even with these levels of flux, the resultant braze using priorart connector blocks can still include porosity within the brazed jointor stitching, i.e., intermittent porosity pockets where the filler metaljoins the materials being brazed together.

In contrast to the undesirable brazeability of the prior art alloyscommonly employed for connector blocks, the connector block of theinvention is highly brazeable. Further, brazing can be successfullydone, i.e., a joint without porosity, stitching or the like, using fluxlevels ranging up to 50 g/m² more preferably 3-20 g/m² and as low as 4to 5 g/m². The low level of magnesium in the inventive alloy minimizesthe formation of magnesium compounds such as magnesium oxide orflouride. Magnesium oxide forms during the brazing process and can bedifficult to remove from the brazed area, thereby compromising theintegrity of the braze. Magnesium flouride, a high melting pointcompound, can be formed by interaction with a flourine-containing flux,such formation also interfering with the brazing process.

The inventive alloy connector block, while having acceptablebrazeability, also has the desired machinability and strength to permitthe connector block to be machined and connected to various othercomponents. The connector block is typically formed by first casting analuminum alloy into a cast shape such as a billet. The billet is thenhomogenized as is known in the art to form a suitable material forextrusion, forging or other hot deformation operation. The shape is thenhot deformed, for example, extruded, into an elongated workpiece. Thehot deformed workpiece is cut into pieces of selected width. Thesepieces are then machined to form the desired passageways, contours,recesses, seats, threads or whatever other configurations are necessaryso that the connector block can interface with a heat exchanger, atubing connector or other components related thereto.

The extruded connector block should have the machinability to enable thenecessary passageways and the like to be formed therein. The inventivealloy combines machinability without the loss of the necessary strengthand ductility for connector block use. To demonstrate the uniqueproperties of the connector block material, various alloy compositionswere tested for machinability. The machining tests, using an AA6061aluminum alloy as a base alloy for comparison purposes, turned one inchdiameter bars downed to 0.900 inch in one pass on a lathe. Sample barswere turned on a lathe, running at 2000 RPM with a feed rate of 0.021inches per minute and a cut depth of 0.050 inches, and using a carbidetool, for approximately 8 inches in length. A second test was conductedwherein the samples were drilled using a ¼ inch drill bit, the bit runat 2000 RPM and the same feed rate as stated above. The drilled holeextended about one inch into each sample. No chip breaker or coolant wasused in either test. As can be seen from Table II, Alloys C-H and J-Nall exhibited desirable machining properties, i.e., small chip or smallcurl-shaped machining debris. Alloys D, H and L-M showed particularlyimpressive machining capabilities. The alloys showing desirablemachining properties also exhibited acceptable strength properties. Forexample, comparing Alloy B with Alloy C, Alloy C has significantlybetter machinability with comparable strength and elongation values. Acomparison between Alloy I with Alloys J-N reveals a similar finding.These comparisons demonstrate that the alloys of the invention providethe necessary machinability without compromising the mechanicalproperties needed when using the alloy in a connector block application.

TABLE II Machining Machining UTS YS Debris (turning) Debris (Drilling)Machining ALLOY (KSI) (KSI) % ELONG. SIZE SHAPE SIZE SHAPE Element(s) A22.8 17.3 33.5 long thickened two long compacted none strings chipsstrings B 27.9 19.9 28.5 long thickened two long strings none stringsragged strings C 26.4 19.1 30.0 small/ chips/ Bi medium strings chips D27.7 21.1 20.0 small single small chips Sn curls E 29.3 22.2 18.0 smallchips/curls small chips Sn, In F 23.9 15.8 29.0 small chips small chipsSn, In G 23.5 15.7 31.5 small chips/curls Bi H 24.0 15.2 29.0 very chipsvery small chips Sn small I 27.4 19.5 26.5 long/ stringy two longcompacted none stringy chips strings J 27.3 20.5 23.5 very curls/chipssmall chips Sn, In small K 25.3 17.7 28.5 small chips with long stringsBi some strings compacting L 26.2 17.6 20.0 small chips very small chipsSn M 26.1 18.7 23.5 small curls very small chips Sn, Bi N 26.5 20.5 25.5small curls small chips Sn, Bi 6061 medium curls small/ broken lengthmedium chips/some curls strings short curls

One of the more important strength requirements for the connector blockis the ability to withstand the application of a torque. In manyapplications, threaded studs are attached to the connector block body bythreading them into complementary threaded bores. The threaded studs arethen used to attach a connector block connector that may hold the fluidsupply and takeaway lines together or facilitate attachment to a supportmember. Thus, the connector block body must be able to receive the studswithout stud stripping during installation. In one application, thestuds may be subjected to approximately 40-60 inch pounds of torqueforce during installation and must withstand approximately 200 inchpounds of force without stripping.

Alloys A and F-H were tested for torque strength to demonstrate thatthey had the requisite strength to meet the connector blockspecification outlined above. A tapped bore, i.e., 8 mm diameter×1.25 mmpitch, was formed in each alloy sample. The sample was held in a viseand threaded studs were torqued into the bore using a torque load of 48inch pounds (5.4 Nm). No failures occurred. The torque was raised to amaximum of 200 inch pounds (22-23 Nm). No thread failure occurred,thereby showing that the inventive alloys still had the necessarystrength to meet the connector block torque specifications.

The free machining elements of bismuth, indium and tin can improvemachinability via three different mechanisms. First, when a freemachining element is used alone, the element exists in the matrix of thealloy material as an individual dispersoid. When the material is beingmachined and a tool contacts a locale containing one or more of thedispersoids, the matrix material and the dispersoids flow differentlywith respect to each other. A mismatch of displacement occurs betweenthe two different materials thereby causing the materials to separatefrom each other upon application of the machining force. This separationresults in void formation. Further interaction causes coalescing of thevoids which then results in material being separated from the workpiece,i.e., chip formation, during machining.

Second, when at least two free machining elements are used, e.g.,bismuth and tin or tin and indium, a low melting point compound can beformed in the matrix. With this low melting point compound present inthe alloy, a local increase in the alloy temperature due to machining ofan article made from the alloy brings the low melting point compound toa soft or liquid state. In this state, the low melting point compoundloses its strength thereby facilitating the formation of small machiningdebris such as one or more chips. The chips can then be easily removedfrom the machining area without interfering with the machiningoperation.

Third, since the free machining elements are relatively low meltingpoint materials, elemental melting or softening can occur duringmachining. This phenomenon can occur particularly when the machiningoperation is severe so as to cause a significant temperature rise in theworkpiece. The melting or softening of the free machining elementscauses the same effect as described above for low melting pointcompounds to enhance machining debris removal.

The inventive alloy also exhibits corrosion resistance which is requiredfor materials for use in heat exchanger applications as evidenced byexcellent corrosion test results in SWAAT testing as described in ASTMG85 Annex 3. Even better corrosion resistance can be achieved byutilizing the inventive composition when controlling titanium levelsbetween 0.07 and 0.3%, more preferably 0.1 and 0.2%, see Alloys O, P andQ in Table I.

The comparisons and test work described above demonstrate that thealuminum alloy article of the invention can be machined, subjected tothe application of torquing forces and brazed to form part of a heatexchanger assembly. Further, the brazing operation can be performed atflux levels significantly lower than methods presently used in the priorart.

While a connector block is illustrated as one type of a heat exchangerarticle requiring machining, corrosion resistance, strength andbrazeability, other articles or components requiring the same propertiescan be made with the compositions described above.

Each and every element in this application can be replaced in part orwhole by another element which will functionally provide the same effectas the specifically described elements. As an example titanium in thealloy may be replaced by vanadium or hafnium or zirconium, or anotherelement with similar properties, to provide the same functionality astitanium in improving corrosion resistance of the alloy. Similarly,indium, tin and bismuth may be replaced in part or whole by otherelements which essentially provide the same functional effect.

As such, an invention has been disclosed in terms of preferredembodiments thereof which fulfill each and every one of the objects ofthe present invention as set forth above and provides a new and improvedaluminum alloy composition and an article made therefrom and a method ofbrazing.

Of course, various changes, modifications and alterations from theteachings of the present invention may be contemplated by those skilledin the art without departing from the intended spirit and scope thereof.It is intended that the present invention only be limited by the termsof the appended claims.

What is claimed is:
 1. A magnesium free aluminum alloy article having amachined opening therein, and having a free machining compositionconsisting essentially of, in weight percent, up to about 0.6% silicon,up to about 1.2% iron, up to about 0.7% copper, between about 0.1% and1.8% manganese, up to about 0.4% chromium, up to about 0.4% zinc, up toabout 0.2% zirconium, between about 0.03 and 0.4% titanium, and eitherbismuth alone as the one free machining element or bismuth and tin asfree machining elements, wherein each of the bismuth and tin is up toabout 1.5%, with the balance being aluminum and incidental impurities.2. The article of claim 1, wherein silicon is up to 0.2%, iron is up toabout 0.7%, copper is up to about 0.5%, manganese ranges between about0.2 and 1.7%, chromium is up to about 0.2%, zinc, is up to about 0.25%,titanium ranges between about 0.03 and 0.3%, tin and bismuth are each upto about 1.3%.
 3. The article of claim 2, wherein silicon ranges between0.03 and 0.12%, iron ranges between 0.03 and 0.12%, copper rangesbetween about 0.1 and 0.5%, manganese ranges between about 0.5 and 1.6%,chromium is up to about 0.1%, titanium ranges between about 0.03 and0.2%, tin and bismuth are each up to about 1.0%.
 4. The article of claim3, wherein silicon ranges between 0.03 and 0.09%, iron ranges between0.03 and 0.15%, copper ranges between about 0.1 and 0.4%, manganeseranges between about 1.0 and 1.6%, titanium ranges between about 0.1 and0.2%, and tin is up to about 0.75%.
 5. The article of claim 1, whereinthe silicon is in a finite amount up to about 0.2%, the iron is in afinite amount up to about 0.7%, and the copper is in a finite amount upto about 0.5%.
 6. The article of claim 5, wherein silicon ranges between0.01 and 0.15%, iron ranges between 0.01 and 0.5%, and copper rangesbetween about 0.01 and 0.4%.
 7. The article of claim 5, wherein copperranges between about 0.01 and 0.4%.
 8. The article of claim 1, whereinthe at least one machining element comprises bismuth and tin.
 9. Thearticle of claim 1, wherein the at least one machining element isbismuth alone.
 10. The aluminum alloy article of claim 1, wherein thearticle is a heat exchanger component.
 11. In a heat exchanger assemblyhaving a plurality of cooling tubes interconnected between a pair ofheaders, adjacent cooling tube separated by fins, and at least oneconnector block having a machined portion therein and being brazed toone of the headers so that a passageway in the connector block is incommunication with one of an inlet and an outlet of one of the headers,the improvement comprising the at least one connector block being analuminum alloy article having a composition as in claim
 1. 12. In amethod of brazing an article to a substrate using a flux, theimprovement comprising forming the article of the aluminum alloycomposition as in claim
 1. 13. The method of claim 12, wherein the fluxapplied is an amount of up to 50 grams of flux per square meter of areato be brazed.
 14. The method of claim 13, wherein the flux amount is upto 20 g/m².
 15. The method of claim 13, wherein the brazing is furnacebrazing.
 16. An aluminum alloy composition consisting essentially of, inweight percent, silicon between 0.03 and 0.12%, iron between 0.03 and0.12%, copper between about 0.1 and 0.5%, manganese between 0.5 and1.6%, up to about 0.7% magnesium, up to about 0.1% chromium, up to about0.4% zinc, up to about 0.2% zirconium, between about 0.03 and 0.2%titanium, an amount of bismuth as the sole free machining element, thebismuth amount up to 1.0%, with the balance being aluminum andincidental impurities.
 17. The composition of claim 16, wherein, zinc isup to about 0.25%.
 18. The composition of claim 16, wherein siliconranges between 0.03 and 0.09%, copper ranges between about 0.1 and 0.4%,manganese ranges between about 1.0 and 1.6%, magnesium ranges from amagnesium free state to an amount up to about 0.3%, and titanium rangesbetween about 0.1 and 0.2%.
 19. The composition of claim 16, wherein,copper ranges between about 0.1 and 0.4%, and the magnesium is from zeroto up to 0.4%.
 20. The composition of claim 16, wherein the magnesium isfrom zero to up to 0.35%.
 21. An aluminum alloy article having thecomposition of claim
 16. 22. The aluminum alloy article of claim 21,wherein the article has a machined portion therein.
 23. The aluminumalloy article of claim 22, wherein the article is a connector block fora heat exchanger assembly.
 24. In a method of brazing an article to asubstrate using a flux, the improvement comprising forming the articleof the aluminum alloy composition of claim
 16. 25. The method of claim24, wherein the flux is applied in an amount up to 50 grams of flux persquare meter of area to be brazed.
 26. The method of claim 25, whereinthe flux amount is up to 20 grams of flux per square meter of area to bebrazed.
 27. An aluminum alloy composition consisting essentially of, inweight percent, silicon between 0.03 and 0.12%, iron between 0.03 and0.12%, copper between about 0.1 and 0.5%, manganese between 0.5 and1.6%, up to about 0.7% magnesium, up to about 0.1% chromium, up to about0.4% zinc, up to about 0.2% zirconium, between about 0.03 and 0.2%titanium, an amount of bismuth and tin as free machining elements, thebismuth and tin amounts each ranging up to 1.0%, with the balance beingaluminum and incidental impurities.
 28. The composition of claim 27,wherein zinc is up to about 0.25%.
 29. The composition of claim 27,wherein silicon ranges between 0.03 and 0.09%, copper ranges betweenabout 0.1 and 0.4%, manganese ranges between about 1.0 and 1.6%,magnesium ranges from a magnesium free state to an amount up to about0.3%, and titanium ranges between about 0.1 and 0.2%.
 30. Thecomposition of claim 27, wherein copper ranges between about 0.1 and0.4%, and the magnesium is from zero to up to 0.4%.
 31. The compositionof claim 27, wherein magnesium is from zero to up to 0.35%.
 32. Analuminum alloy article having the composition of claim
 27. 33. Thealuminum alloy article, of claim 32 wherein the article has a machinedportion therein.
 34. The aluminum alloy article of claim 33, wherein thearticle is a connector block for a heat exchanger assembly.
 35. In amethod of brazing an article to a substrate using a flux, theimprovement comprising forming the article of the aluminum alloycomposition of claim
 27. 36. The method of claim 35, wherein the flux isapplied in an amount up to 50 grams of flux per square meter of area tobe brazed.
 37. The method of claim 36, wherein the flux amount is up to20 grams of flux per square meter of area to be brazed.
 38. An aluminumalloy article having machined opening therein and a free machiningcomposition consisting essentially of, in weight percent, up to about0.6% silicon, up to about 1.2% iron, up to about 0.7% copper, betweenabout 0.1% and 1.8% manganese, up to about 1.5% magnesium, up to about0.4% chromium, up to about 0.4% zinc, up to about 0.2% zirconium,between about 0.03 and 0.4% titanium, an amount of indium and tin asfree machining elements, the indium ranging between 0.05% and 0.5%, andthe tin amount ranging up to 1.5%, with the balance being aluminum andincidental impurities.
 39. The machined article of claim 38, whereinsilicon is up to 0.2%, iron is up to about 0.7%, copper is up to about0.5%, manganese ranges between about 0.2 and 1.7%, magnesium is up toabout 0.8%, chromium is up to about 0.2%, zinc, is up to about 0.25%,titanium ranges between about 0.03 and 0.3%, and the tin amount is up to1.3%.
 40. The machined article of claim 39, wherein silicon rangesbetween 0.03 and 0.12%, iron ranges between 0.03 and 0.12%, copperranges between about 0.1 and 0.5%, manganese ranges between about 0.5and 1.6%, magnesium is up to about 0.7%, chromium is up to about 0.1%,titanium ranges between about 0.03 and 0.2%, and the tin amount is up to1.0%.
 41. The machined article of claim 40, wherein silicon rangesbetween 0.03 and 0.09%, iron ranges between 0.03 and 0.15%, copperranges between about 0.1 and 0.4%, manganese ranges between about 1.0and 1.6%, magnesium ranges from a magnesium free state to an amount upto about 0.3%, and titanium ranges between about 0.1 and 0.2%.
 42. Themachined article of claim 38, wherein the silicon is more than zero andup to about 0.2%, the iron is more than zero and up to about 0.7%, andthe copper is more than zero and up to about 0.5%.
 43. The machinedarticle of claim 42, wherein silicon ranges between 0.01 and 0.15%, ironranges between 0.01 and 0.5%, copper ranges between about 0.1 and 0.4%,and the magnesium is from zero to up to 0.4%.
 44. The machined articleof claim 42, wherein copper ranges between about 0.01 and 0.4%, and themagnesium is from zero to up to 0.35%.
 45. The machined article of claim38, wherein titanium ranges between 0.07 and 0.3% to enhance corrosionresistance as measured using ASTM G85 Annex
 3. 46. The machined articleof claim 38, wherein the article is a connector block for a heatexchanger assembly.
 47. In a method of machining an opening in articlefor use in a heat exchanger assembly, the improvement comprisingmachining the opening in an article having the composition of claim 38.